1. Field of the Invention
This invention relates to substrate processing, and more particularly, to a high resolution, high precision collimating shadow mask and a method of utilizing such a mask to fabricate a patterned organic light emitting diode (OLED) micro-display.
2. Description of the Related Art
Shadow masks were developed for use in manufacturing cathode ray tube displays for televisions. Early shadow masks consisted of a metal plate punched with tiny holes that separate the colored phosphors in the layer behind the front glass of the screen. Three electron guns at the back of the screen sweep across the mask, with the beams only reaching the screen if they pass through the holes. As the guns are physically separated at the back of the tube, their beams approach the mask from three slightly different angles, so after passing through the holes they hit slightly different locations on the screen.
The screen is patterned with dots of colored phosphor positioned so that each can only be hit by one of the beams coming from the three electron guns. For instance, the blue phosphor dots are hit by the beam from the “blue gun” after passing through a particular hole in the mask. The other two guns do the same for the red and green dots. This arrangement allows the three guns to address the individual dot colors on the screen, even though their beams are much too large and too poorly aimed to do so without the mask in place.
Over the years, as new types of displays have been developed and technologies have evolved for manufacturing displays, the types of shadow masks and the manner in which same are used have changed. Shadow masks are now commonly used in the manufacture of digital displays. However, the current technology for making full color high resolution OLED micro-displays is limited to having a white OLED emitter patterned by color filter layers. Given the current state of the art, this technology is the most feasible way to fabricate full color high resolution OLED micro-displays.
The problem with this type of micro-display is the loss of light emission efficiency. The color filters transmit only about 20% of the light and the rest is absorbed in the filters. This leads to dimmer micro-displays, not suitable for many applications where high luminance is required, such as daylight displays.
An obvious solution to this problem is to remove the color filters but still retain the individually addressable R, G and B primary color sub-pixels. This can be achieved if the white OLED emitter is replaced by individually patterned R, G and B color OLED sub-pixels.
Such methods have been developed and utilized for large area displays which typically have large sub-pixels. For example, LITI (Laser Induced Thermal Imaging) is one of the methods for transferring OLED materials in a patterned form. However, this method is only suitable for large area displays with large sub-pixels, where the dimensional and positioning accuracy is less demanding. When smaller sub-pixels are being created, blurring or “feathering” of the light beam which forms the sub-pixels on the silicon wafer occurs substantially degrading the performance of the display.
Another problem with the LITI method is the change in stoichiometry of the organic materials transferred, which results in compromised display performance. Another method which has been successfully used in patterning large area OLED displays uses a contact metal shadow mask. However, this technology suffers from resolution issues and is not suitable for patterning sub-pixels smaller than 10 by 10 microns.
The present invention relates to a novel high resolution, high precision collimating shadow mask which is uniquely suited for fabrication of smaller patterned OLED micro-displays and to a method of manufacturing smaller patterned OLED micro-displays utilizing the mask. The high precision, high resolution shadow mask of the present invention can be made of Si, Si and Si3N4, Si and SiO2 or other oxides and materials of high strength and dimensional stability.
It is, therefore, a primary object of the present invention to provide a high precision, high resolution collimating shadow mask.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask capable of providing sharp and precise definition of the edges of the deposited areas on the substrate without contacting the substrate.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask capable of eliminating or substantially reducing feathering or image shift due to the angle of deposition.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask wherein feathering is reduced by increased mask thickness or reduced sub-pixel size.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask wherein image shift is reduced through the formation of square shaped sub-pixels.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask capable of achieving high dimensional and positional accuracy without requiring that the mask and substrate be perfectly flat.
It is another object of the present invention to provide a high precision, high resolution collimating shadow mask capable of achieving high dimensional and positional accuracy without requiring the gap between the mask and substrate be perfectly uniform.